1. Field of the Invention
The present invention relates to an image reading device by which an image signal, recorded in a recording medium, is sensed using a line sensor, for example.
2. Description of the Related Art
Conventionally, there is known an image reading device, sensing an image signal using a line sensor, in which an illumination mechanism is provided with a light source comprising multiple light-emitting diodes to ensure that an adequate amount of light is received by the line sensor, and also a divergent optical system is provided so that the unevenness of the amount of light is equalized. Further, in an image reading device disclosed in Japanese Unexamined Patent Publication No. 8-167972, the light-emitting diodes are arranged on two separate lines, and a superposing optical system is provided to superpose light beams emitted by the two lines of light-emitting diodes onto a single line corresponding to the line sensor.
In the illumination mechanisms, however, many optical members are needed, and thus the construction is complex.
On the other hand, in a sensing method utilized in the image reading device whereby a focal point is detected, there is known a method by which, based on an image signal read by the line sensor, a contrast of the image is calculated, and the focal point is detected in accordance with the peak value of the contrast. The contrast is obtained by subtracting a filtered signal, which is obtained by applying a low-pass-filtering process to the image signal, from the image signal, and integrating the filtered signal.
In the sensing method, however, it is necessary to carry out a complicated calculation in the low-pass-filtering process, and it is necessary to consider whether a frequency characteristic of an object to be read is changed. Further, if the image signal contains noise, the peak value of the contrast cannot be calculated exactly, since the noise, for example, is also integrated.
Therefore, an object of the present invention is to provide an illumination optical device in which the number of optical members is reduced to simplify construction.
According to the present invention, there is provided an illumination optical device, mounted in an image reading device, comprising a plurality of light-emitting elements and an optical system.
The plurality of light-emitting elements are arranged on a straight line. The light-emitting elements radiate light beams of color components which are different from each other. The optical system is disposed such that the optical axis of the optical system is perpendicular to the straight line, so that the light beams are radiated onto a recording medium.
Further, according to the present invention, there is provided an image reading device comprising a light source, a first optical system, an imaging device, a second optical system, an out-of-register detecting processor and a moving mechanism.
The light source radiates first, second and third light beams having first, second and third color components, respectively. The first optical system changes the first light beam to a first parallel beam, which is parallel to the optical axis of the first optical system, and changes the second and third light beams to second and third parallel beams, respectively, which are inclined to the optical axis. The first, second and third parallel beams are led to a recording medium in which an image is recorded. The imaging device, which includes a light receiving surface on which the image is formed, outputs pixel data corresponding to the image. The second optical system forms the image on the light receiving surface based on the first, second and third parallel beams becoming incident on the recording medium. The out-of-register detecting processor detects an out-of-register value in accordance with the pixel data, which is a deviation between first and second portions on the light receiving surface. The first portion is illuminated by a light beam corresponding to the first parallel beam radiated on an area of the recording medium, and also the second portion is illuminated by a light beam corresponding to one of the second and third parallel beams radiated on the area. The moving mechanism moves either the imaging device or the recording medium along the optical axis of the first optical system in accordance with the obtained out-of-register value.